#log_line_prefix = ''         # e.g. '<%u%%%d> '
                              # %u=user name %d=database name
                              # %r=remote host and port
                              # %p=PID %t=timestamp %i=command tag
                              # %c=session id %l=session line number
                              # %s=session start timestamp
                              # %x=stop here in non-session processes
                              # %%='%'

Andrew Dunstan